Health insurers participating in the new Marketplaces are filing rates for 2015 during the next few months. A few states have already released data on proposed rates. There is substantial economic, policy, and political interest in the magnitude of proposed rate changes. This brief provides background for understanding the economic drivers of proposed rates, state and federal rate review authority, the effects of rate changes on Marketplace enrollees and federal spending on premium credits, and the economic and political dynamics of the rate review and approval process.